1. Field of the Invention
The present invention relates to a wafer processing method for removing a chamfered portion formed along the outer circumference of a wafer and next reducing the thickness of the wafer to a predetermined thickness.
2. Description of the Related Art
A plurality of devices such as ICs and LSIs are formed on the front side of a semiconductor wafer so as to be partitioned by a plurality of crossing division lines (streets). The back side of the semiconductor wafer is ground by a grinding apparatus to reduce the thickness of the wafer to a predetermined thickness. Thereafter, the semiconductor wafer is cut along the division lines by using a cutting apparatus (dicing apparatus) to thereby obtain the individual devices divided from each other. These devices are widely used in various electrical equipment such as mobile phones and personal computers. The grinding apparatus for grinding the back side of the wafer includes a chuck table for holding the wafer and a grinding unit including a rotatable grinding wheel, which has a plurality of abrasive members for grinding the wafer held on the chuck table. By using this grinding apparatus, the wafer can be ground with high accuracy to obtain a desired thickness.
In grinding the back side of the wafer by using the grinding apparatus, a protective tape is attached to the front side of the wafer for the purpose of protecting the devices formed on the front side of the wafer. However, when the thickness of the wafer is reduced to about tens of micrometers by the grinding step, the wafer cannot be stably supported by a low degree of rigidity of the protective tape, so that the wafer supported to the protective tape becomes flexible as a whole and therefore unstable. Accordingly, there is a problem in handling the wafer in the grinding step and any subsequent steps. To facilitate the handling of the wafer reduced in thickness by the grinding step, there is described in Japanese Patent Laid-open No. 2000-158334, for example, a method including the steps of attaching a rigid support substrate to the front side of a wafer and next grinding the back side of the wafer.
In general, an arcuate chamfered portion is formed along the outer circumference of a semiconductor wafer in the range from the front side to the back side of the semiconductor wafer. Accordingly, when the back side of the wafer is ground to reduce the thickness of the wafer, a knife edge (eaves-like shape) is formed by an arcuate surface of the chamfered portion and a ground surface of the wafer, causing danger and chipping on the outer circumference of the wafer. As a result, there arises a problem that the quality of each device may be reduced or the wafer may be broken. To solve this problem, Japanese Patent Laid-open No. 2000-173961 discloses a semiconductor device manufacturing method including the steps of forming a cut groove on the front side of a semiconductor wafer along the boundary between a flat portion (front side surface) and a chamfered portion formed along the outer circumference of the wafer and next grinding the back side of the wafer so that the thickness of the wafer becomes less than the depth of the cut groove.